A. Field of the Invention
This invention relates to electrically conductive grounding straps or tethers which are attached to the body by way of the individual's limbs in order to ground operating personnel and prevent build-up of static electricity on such persons. More particularly, this invention pertains to the strap means for attaching the ground tether to the body members and maintaining the electrically conductive portion of the strap in intimate electrical contact with the skin of the wearer. The invention is especially concerned with a non-conductive elastomeric fabric or knitted band to the interior surface of which is embroidered a continuous conductive thread, preferrably sewn in a zig-zag or rick-rack pattern, so that the body member may be resiliently embraced in a closed self-adjusting loop.
B. Prior Art
In U.S. Pat. No. 4,398,277, there is shown an elastomeric body strap having a fabric band formed by at least one interlaced yarn which includes an end having an electrically conductive fiber plaited with an end having an elastomeric non-conductive fiber. The conductive yarn and the insulative yarn are plaited or knitted together to form interlocking loops which define two levels, an exterior insulated back with a conductive interior face. The foregoing patent and the references cited therein of record are generally representative of the prior state of the art.
C. Purpose
One of the inherent problems in making a knitted or plaited fabric from yarns of widely different elongation characteristics is in producing a generally uniform interwoven configuration wherein the loops are of consistent size, especially when elastomeric yarns are interlaced with brittle yarns employing metallic filaments. Not only is it desirable that even pressure be exerted upon the conductive yarns in contact with the wearer's skin so that electrical charges may be carried away from operating personnel, but also it is necessary that there be electrical continuity through the conductive yarn to ground. Breaking of the metallic elements as a result of failure of the conductive strands, for example, at the interlacing of the loops, can make the body tether completely inoperative as a consequence of electrical discontinuity.
It is therefore an object of this invention to provide an elastomeric body band for tethering operating personnel to electrical ground.
Another object of this invention is to provide a conductive stretchable body band in which the elastomeric portion urges the conductive portion against the skin of the wearer with uniform pressure.
Yet another object of this invention is to construct a stretchable conductive body band in which the means for attaching the conductive elements to the elastomeric elements provides maximum assurance against conductive strand breakage.
Yet still another object of this invention is to provide an elastomeric insulative body band in which a conductive thread is embroidered upon the surface of the band by a line of stitching wherein an insulative thread component having substantially the same elongation characteristics as the conductive thread component is interlocked with the latter at the interior face of the band.
Other objects of this invention are to provide an improved device of the character described which is easily and economically produced, sturdy in construction and both highly efficient and effective in operation.